With the advancement in scientific technologies and the modularization and miniaturization of camera lens, it is now possible to produce digital cameras having a very small volume, and most of currently available mobile phones are provided with the function of a digital camera. In a miniature lens, there are many different auto-focusing driving mechanisms. Among others, voice coil motor (VCM) is the currently most widely adopted auto-focusing driving mechanism. The VCM has the advantages of small volume, low power consumption, accurately actuated displacement, and cost-effective, and is therefore very suitable for short-distance driving in miniature lens auto-focusing.
FIG. 1 schematically shows a conventional lens focusing mechanism 200 consisting of a lens assembly 201 and a photo sensor 202. With the lens assembly 201, light reflected from an object can form an image on the photo sensor 202. In the case a distance between the lens assembly 201 and the photo sensor 202 is fixed, that is, the lens assembly 201 is a fixed focal lens, only the object located more than two to three meters away from the lens (i.e., located at a hyper focal distance) can be clearly shown on the camera. If it is desired to own the macro shooting function, it is necessary to use an additional lens focusing unit to displace the lens assembly 201, so as to change the distance between the lens assembly 201 and the photo sensor 202 and thereby achieve the purpose of focusing.
In the case the lens assembly 201 is provided with the zoom function, multiple lens groups inside the lens assembly 201 must also be displaced corresponding to the changes in zoom ratio. In this case, the lens focusing mechanism must also be included in the lens module to enable the displacement of the lens groups.
In the conventional focusing mechanism, the lens assembly is displaced mainly via a manually controlled mechanism, and is therefore not so convenient for operation. When the lens is electromagnetically driven, it is possible to achieve the function of automatic focusing and to simplify the design of the lens focusing mechanism. However, the electromagnetically driven lens focusing mechanism would cause the problem of electromagnetic interference (EMI). For the electromagnetically driven lens focusing mechanism to be widely applied on mobile phones, notebook computers, and personal digital assistants (PDAs) that are required to comply with the rules and regulations concerning electromagnetic interference (EMI), electromagnetic compatibility (EMC), and electrostatic discharge (ESD), it is necessary to overcome the EMI problem with the electromagnetically driven lens focusing mechanism.
Therefore, it is tried by the inventor to develop an EMI-proof miniature lens focusing mechanism that not only has simplified mechanism design, reduced manufacturing cost, and improved assembly process, but also complies with the rules and regulations concerning EMI, EMC, and ESD, and can therefore be applied in the camera modules for mobile phones, notebook computers, and PDAs.